This disclosure describes an innovative plasma based adaptive optics approach that improves the performance of optical systems by reducing external optical distortions.
Adaptive optics (AO) is generally used to improve the performance of optical systems by reducing the effect of wavefront distortions. In some examples, adaptive optics is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, or in retinal imaging systems to reduce the impact of optical aberrations. Adaptive optics works by measuring the distortions in a wavefront and compensating for them with a spatial phase modulator such as a deformable mirror (DM) or liquid-crystal devices (LCDs).
Current adaptive optics approaches involve deformable mirrors including mechanical actuators that oftentimes have limited frequency and spatial resolution. Similarly, known liquid-crystal devices often have limited bandwidth.
For instance, two known technologies have been embraced by the adaptive optics community, deformable mirrors and light emitting diode (LED) current pulse measurement systems (LCPMS). Deformable mirrors typically use a thin (e.g., 1 mm or less) continuously reflective surface that is manipulated by ceramic, piezoelectric, or electrostrictive actuators to modify the wavefront. These actuators are usually expensive, which limits the number that can be used and thus the overall spatial resolution of the minor, and are restricted to low frequencies due to their mechanical inertia. Microelectromechanical systems (MEMS) based deformable mirrors have been developed, but these system offer only limited improvements in bandwidth.
LCPMs, meanwhile manipulate wavefronts in a local manner. LCPMs do offer the advantage over deformable minors in that they are able to correct wavefronts providing high levels of spatial resolution, but they offer low bandwidth. In addition, LCPM techniques typically have problems arising due to polarization dependence, pixilation, high chromaticity of the corrected wavefront, and low correction capabilities.
The two challenges facing adaptive optics technology for practical use are the spatial and temporal resolution provided by the wavefront correction device, although each industry, such as, healthcare, military, astronomy, etc. may have different requirements for both. For example, applications in free-space secure communications and astronomy require very high bandwidth due to the inherent nature of the atmospheric turbulence, whereas, in the application of retinal scanning, very high spatial resolution is required to visualize the retina properly.
Laser communications and aero-optics are particularly challenging applications because of the high frequency nature of the distortion caused by the high speed flow that passes over the lens. The light source consists of a laser that is mounted on the fuselage of an aircraft. The laser beam is distorted by disturbances in the external flow passing over the aperture of the lens. Generally, two types of flows are responsible for aero-optical aberrations, high-speed shear layers and boundary-layers. These flows are optically active and produce time-varying near-field wavefront aberrations with high-frequency content.
Thus, there is a need for adaptive optics that improves the performance of known optical systems, while addressing the varying requirements of applications requiring adaptive optics systems.